With various forms of commercial platforms in which passengers are transported, minimizing noise inside a cabin of the mobile platform is an important consideration. In applications involving commercial passenger aircraft, this is an especially important consideration. The cabin noise within a commercial aircraft is caused at least in part by the turbulent boundary layer flow over the skin of the aircraft. This is especially so when the aircraft is traveling at cruise speeds (e.g., around 500 mph or slightly greater), and at an area within the fuselage generally between the nose and wings.
It would be highly advantageous and desirable if an additional degree of noise reduction could be accomplished without simply adding additional insulation into the construction of a fuselage or other cabin-like structure of a high speed mobile platform. As will be appreciated, the adding of insulation increases the weight of the mobile platform, as well as its cost of manufacture. The additional weight added to the mobile platform by simply adding extra insulating material into the fuselage also increases the overall weight of the mobile platform, and therefore contributes to a reduction in fuel economy.
In one aspect the present disclosure relates to a method for reducing noise and vibration within a structure of a mobile platform, wherein the noise and vibration are at least in part caused by airflow over an outer skin of the mobile platform parallel to a longitudinal line extending fore to aft along the structure. The method may comprise forming the structure such that a fundamental panel vibration mode shape of the structure is not parallel to the longitudinal line.
In another aspect the present disclosure relates to a method for reducing noise within a mobile platform, wherein the noise is at least in part caused by a turbulent boundary layer flow of air over an outer surface of a skin of the mobile platform. The method may comprise forming a fuselage of the mobile platform with a plurality of stringers and a plurality of frame members. The fuselage may be further formed so that both the plurality of stringers and the plurality of frame members are oriented at non-parallel to a longitudinal axis extending fore to aft along the fuselage. A skin may be secured to at least a subplurality of the stringers and a subplurality of the frame members, for supporting the skin. The structure may be further assembled such that the structure is fastened to and supports the skin to provide a fundamental vibration mode shape for the skin that is not parallel to a direction of flow of the turbulent boundary layer flow.
In still another aspect a method is disclosed for reducing noise and vibration within a fuselage of a mobile platform, wherein the noise and vibration are at least in part caused by airflow over an outer skin of the mobile platform parallel to a longitudinal line extending fore to aft along the fuselage of the mobile platform. The method may comprise forming a fuselage with a plurality of stringers and a plurality of frame members such that at least one of the plurality of stringers or the plurality of frame members is oriented parallel to the longitudinal line. The fuselage may be formed with a plurality of stiffening members that are oriented at an angle non-parallel to the longitudinal line, non-parallel to the plurality of stringers and non-parallel to the plurality of frame members. A skin panel may be secured to the pluralities of stringers, frame members and stiffening members. The non-parallel orientation of the stiffening members relative to the longitudinal line is used to create a fundamental panel vibration mode shape for the skin of the fuselage that is not parallel to the longitudinal line, to cause a noise reduction within an interior area of the fuselage of noise generated by airflow over the skin of the fuselage while the mobile platform is in flight.